Wideband dual-slot waveguide array

ABSTRACT

A slotted waveguide array having a unique dual-slot configuration which significantly increases the bandwidth and scanning angle capability of a linear waveguide slot array. The pattern of the array sub-group has a null in the direction at which a grating lobe would normally occur. With the grating lobe suppressed in this manner, slot conductances are stable with frequency. The result is good pattern integrity and high antenna efficiency.

United States Patent [1 1 Nemit June 19,1973

l l WIDEBAND DUAL-SLOT WAVEGUIDE ARRAY [75] inventor: Jeffrey T. Nemit, Canoga Park, Calif.

[73] Assignee: International Telephone and A v Telegraph Corporation, New York,

[52 7 us. c|. 343/771, 343/844 51 Int. Cl. H0lq 13/10 58 Field of Search 343/771,:344

[56] References Cited UNlTEDfSTATESLPATEN-TS 2,906,363 9 1959 Clay 343/844 DUQL SLOT eno/m-oxas 3,100,300 8/l963 Slcttcn. 343/77! Primary ExaminerEli Lieberman Attorney-C. Cornell Remsen, Jr., Walter J Baum,

Thomas E. Kn'stofferson et al.

[57] ABSTRACT A slottedwaveguide array having a unique dual-slot configuration which significantly increases the bandwidth and scanning angle capability of a linear waveguide slot array. The pattern of the array sub-group has a null in the direction at which a grating lobe would normally occur. With the grating lobe suppressed in this manner, slot conductances are stable with frequency. The result is good pattern integrity and high antenna efficiency. I

10 Claims, 2 Drawing Figures PAIENIEB M I 9 I".

QOkUQQQQ BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to directive antenna arrays, and more particularly, to means and techniques for widening the frequency passband and width of scan angle achievable in an inertialess scanning system.

2. Description of the Prior Art Linear waveguide slot arrays are of themselves wll known and have been used as line sources to provide directive beams. Such arrays find various applications in the radar field, for example, they may be combined to form an area or planar array to produce a directable pencil beam. A typical linear waveguide slot-array as known inthe prior art as illustrated in FIG. 1. In the textbook- Radar Handbook by Merrill I. Skolnik, McGraw-I-Iill 1970) Chapter. 13, is devoted to the subject of frequency-scanned arrays. The linear slot-array with which the present invention is concerned, is particularlyuseful in the area of frequency (inertialess scanning. An illustration on Page 13-12 of the aforementioned text shows a planar, or area type array, assembled from just such prior art linear-slot waveguide array subcombinations as illustrated at FIG. 1.

Typically, the slot radiators are loosely coupled to the waveguide, the actual amount of coupling being controlled by the slot angle 0. Moreover, the realtive phase of energy contributed to the aperture from a givenslot may be controled in accordance with the sense of the slot angle 0.

In general, there are two modes of operation for traveling wave arrays of this type. In the first mode, slots are cut at regularly spaced close intervals, this resulting in a beam direction nearly endfire. In the second type, slots are cut at approximately one-half guidewavel ength intervals, to give a nearly broadside beam radiation characteristic. Alternating the slots, as illustrated in FIG. 1, provides the required 180 reversal of excitation between adjacent slots placed in accordance with this secondmode of operation.

-In a broadside array of the foregoing type used for frequency scanning, two system variables basically determine the slot array geomtry. These variable are beam position-and change of beam position asa function of frequency. These two parameter uniquely define the following two design parameter, namely, the feedline propagation constant (K which for a waveguide, is determined primarily by the waveguie a dimension; and secondly, the slot spacing (s) which is normally greater than one-half wavelength but less than one wavelength. For conditions of the design parameters and frequency of excitation placing the main beam nearly normal to the array, no grating lobes are formed in real space. As thebeam is scanned away from normal, as a result of a change in frequency, however, a grating lobe will appear in realspace. The'appearance of this second (grating lobe) in real space, limits the bandwidth and scan range of this type of array for three reasons. First, the extra lobe reduces the gain of the principal beam, in that it diverts energy which it is desired to place in the main beam. Second, its appearance drastically changes the individual slot conductances, which in turn degrades the excitation and efficiency. Third, it represents a side-lobe of significant amplitude and that is nearly always undesirable from a system point of view.

The manner in which the present invention provides an unique solution to the aforementioned inherent problems in the type of antenna with which the present invention is concerned, will be apparent as this disclosure proceeds.

SUMMARY OF THE INVENTION The present invention involves the use of multiple slots arranged in subgroups. Each of the subgroups constitutes a radiator of two or more radiating elements. As illustrated and described hereinafter, each of these subgroups contains two slots, since that configuration achieves the desired result with a minimum of cost and complexity. More than two slots or radiating elements per subgroup, could, of course, be used to achieve a similar result. The basis of operation in suppressing the so-called grating lobe is that the pattern of the array subgroup contains a null in the direction at which a grating lobe would normally occur in a comparable prior art linear (single element .per radiator) array. With the grating lobe suppressed, the slot conduc-.

tances are stable with frequency and good pattern integrity and increased antenna efficiency results.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION or THE PREFERRED EMBODIMENT As hereinbefore indicated, FIG. 1 is a drawing of a prior art waveguide slot-type array having a plurality of slot radiators uniformly spaced by a common spacing or distance 5. The alternately angled slots provide alternate phase sense between adjacent radiators, the slot angle 0 being either positiveor negative as arbitrarily indicated. A

Referring now to FIG. 2, a wideband dual-slot waveguide array in accordance with the present invention, is illustrated. The same convention in respect to the angle 0 of the slots is indicated. The slot subgroups or radiators consist of two slots or radiating elements each. The subgroup spacing s is measured from a corresponding part of each slot, for example, from center to center of typical slots 1 and .2, forming a subgroup. The radiator spacing s is shown typically between radiating elements 3 and 4 belonging respectively to subgroups 5 and 6. The slanting or angling of the slots in FIG. 2 is for the same purpose of as indicated in connection with FIG. 1, however, it should be understood that the slot angle for each radiating element of a subgroup, for example, of slots 1 and 2, would be the same.

The spacing s is determined by sytem parameters previously discussed, i.e., beam positioning considerations. The spacing between elements in the subgroup is illustrated as s, and isselected so that the dual-slot element pattern will produce a null in the direction in which a grating lobe would normally occur for the single radiating element slot arrangement of FIG. 1, assuming all other characteristics of FIG. 1 and FIG. 2 were the same. The element pattern of a subgroup with equal amplitude excitation is: p,,(u) cos [SI/2 (kg-k0 u)], where u sin0,

kg propagation constant of feed (2 Ir/Ag) and k free-space propagation constant (2 rr/Ao). It follows from the array geometry that and k0 ug= kg 3 IT/S2 where no sin of angle of main beam, and

ug sin of angle of first grating lobe to enter real space with frequency scanning.

The strengths of themain beam and grating lobe are p (uo) cos [SI/2S2 1r] and p (ug) cos [551/252 1r] For a complete suppression of the grating lobe It whould be re-emphasized that the dimensions S1 and S2 refer to the equivalent electrical length which may be slightly different from the physical dimensions.

The matter of width of the individual slots is a design consideration susceptible to selection in accordance with well known principles. In this respect, i.e., width and depth of the individual slot cuts, the structure of the present invention follows known criteria.

Those skilled in this art will realize that the invention could be applied to other types of radiating elements structure for accomplishing the objective and function of the present invention which fall within the spirit and scope of the present invention will suggest themselves to those skilled in this art, once the principles hereof are understood. Accordingly, his not intended that the specific embodiment/illustrated and described, should be considered as limiting the scope of the present invention. The drawings and th'is'description are to be regarded as typical and illustrative only.

What is claimed is:

l. A linear antenna array having a plurality of radiating elements fed from successive points along a transmission line, and comprising the combination of:

a first set of said radiating elements in which the individual elements thereof are spaced by a first spacing factor, said first spacing factor being. chosen in accordance with parameters including predetermined beam position and angular beam scan sensitivity as a function of frequency} and a second set of said radiating elements in which the individual elements thereof are spaced along said transmission line first spacing factor, said second set being offset along said transmission line by a second spacing factor with respect to said first set, said second spacing factor being such that the field at the antenna aperture resulting from both of said sets of radiating elements do not produce a grating lobe at a beam andle at which such a lobe would be generated as a result of radiation by said first set in the absence of said second set.

2. A linear antenna array for frequency or phase scanning, comprising:

a transmission line; first means comprising a plurality of radiators fed from successive pointsv mutually spaced a first distance'along said transmission line for establishing a predetermined relationship of beam angle versus excitation frequency;

second means within each of said radiators comprising a subsgroup having a plurality of radiating elements mutually spaced by a second distance from each other and having one element of each of said subgroups located at each of said successive points,

said second distance being such as to tend to produce a null at the angle at which a grating lobe would be produced by said first means in the absence of said second means.

3. Apparatus accordingto claim 2 in which said transmission line is a waveguide.

4. Apparatus according to claim 3 in which said waveguide has wide and narrow conductive walls and said radiating elements of said subgroups each com prise a slot in one of said narrow walls, said slots being at a predetermined angle along said narrow wall so as to effect a predetermined coupling and energy phase.

5. Apparatus according to claim 4 in which said slot any radiating element in one subgroup to the corresponding element in the adjacent groups is defined as being not less than one half wavelength and not more than one wavelength for any frequency of excitation within the band of utility of said array.

8. Apparatus according to claim 7 in which said second distance is defined as substantially equal to one third of said first distance.

9. Apparatus according to claim 8 in which said first and second distances are defined as equivalent electrical lengths.

l0. Apparatusaccording to' claim 2 in which said plurality of radiating elements, in each of said subgroups, is equal to two and said second distance is defined as substantially equal to onethird of said first distance. 

1. A linear antenna array having a plurality of radiating elements fed from successive points along a transmission line, and comprising the combination of: a first set of said radiating elements in which the individual elements thereof are spaced by a first spacing factor, said first spacing factor being chosen in accordance with parameters including predetermined beam position and angular beam scan sensitivity as a function of frequency; and a second set of said radiating elements in which the individual elements thereof are spaced along said transmission line first spacing factor, said second set being offset along said transmission line by a second spacing factor with respect to said first set, said second spacing factor being such that the field at the antenna aperture resulting from both of said sets of radiating elements do not produce a grating lobe at a beam andle at which such a lobe would be generated as a result of radiation by said first set in the absence of said second set.
 2. A linear antenna array for frequency or phase scanning, comprising: a transmission line; first means comprising a plurality of radiators fed from successive points mutually spaced a first distance along said transmission line for establishing a predetermined relationship of beam angle versus excitation frequency; second means within each of said radiators comprising a subsgroup having a plurality of radiating elements mutually spaced by a second distance from each other and having one element of each of said subgroups located at each of said successive points; said second distance being such as to tend to produce a null at the angle at which a grating lobe would be produced by said first means in the absence of said second means.
 3. Apparatus according to claim 2 in which said transmission line is a waveguide.
 4. Apparatus according to claim 3 in which said waveguide has wide and narrow conductive walls and said radiating elements of said subgroups each comprise a slot in one of said narrow walls, said slots being at a predetermined angle along said narrow wall so as to effect a predetermined coupling and energy phase. Apparatus according to claim 4 in which said slot angle of said radiating elements of aLternate subgroups is of one sense with respect to a plane perpendicular to said waveguide wide and narrow walls and of the opposite sense with respect to said plane for the subgroups between said alternate subgroups.
 6. Apparatus according to claim 4 in which each of said subgroups comprises two slots thereby providing two radiating elements.
 7. Apparatus according to claim 6 in which said first distance spacing said slot subgroups measured between any radiating element in one subgroup to the corresponding element in the adjacent groups is defined as being not less than one half wavelength and not more than one wavelength for any frequency of excitation within the band of utility of said array.
 8. Apparatus according to claim 7 in which said second distance is defined as substantially equal to one third of said first distance.
 9. Apparatus according to claim 8 in which said first and second distances are defined as equivalent electrical lengths.
 10. Apparatus according to claim 2 in which said plurality of radiating elements, in each of said subgroups, is equal to two and said second distance is defined as substantially equal to one third of said first distance. 